The long-term goal of this project is to define the processes involved in the assembly, multiplication and degradation of mitochondria, and to learn how such processes are controlled. We wish to gain more specific information about the transcription products of yeast mitochondrial DNA and the mechanisms controlling transcription. Cytoplasmic petite mutants of yeast have extraordinarily large changes in the base composition of their mtDNA. One of our goals in this project is to characterize changes in petite mtDNA by DNA-DNA and RNA-DNA hybridization. It is hoped that molecular mapping of mitochondrial DNA can be accomplished by mtDNA-mt-tRNA hybridization, and genetic analysis of several series of these respiratory incompetent cytoplasmic petite mutants. We also hope to further elucidate some of the details of mitochondrial DNA replication in yeast. The information gained from these studies would be used to design experiments to investigate the cytoplasmic-mitochondrial interactions involved in mitochondrial assembly and in the control of mitochondrial mass. We wish to study the control of mitochondrial synthesis and degradation in the yeast system which is most suitable for experimental manipulation, and also in complex mammalian systems, where changes in mitochondrial mass are effected by changes in both synthetic and degradation rates.